Conventional ink jet printing devices operate by squeezing controlled amounts of ink from within a reservoir through a nozzle, such as by varying the reservoir volume with a piezoelectric transducer. However, conventional ink jet printing devices have lacked the capability to produce smooth gray scale images, and the capability to control both the amount of ink deposited and the degree of ink atomization for controlling both the size of the deposited drops and their density. Further, conventional ink jet printing systems have lacked the capability to deposit a wide range of fluids or particles on a wide variety of arbitrarily oriented surfaces.
On the other hand, conventional spray painting devices such as airbrushes produce smooth gray scale images on a variety of surfaces, but have lacked both precision and the capability to produce detailed images rapidly.
In a conventional spray painting apparatus, a fluid is delivered to the surface using a differential pressure (or "siphon feed") mechanism. The siphon effect is produced by a gas stream that flows past an orifice in a spray head. The high velocity gas stream creates a low pressure region near the orifice, which low pressure region draws the deposition medium (which may be ink or paint) out from the spray head through the orifice.
The gas must flow for a sufficient duration to produce sufficiently low pressure to draw the deposition fluid through the orifice. If the flow duration is too short, no fluid will be drawn through the orifice. In order to deposit a single, precisely dimensioned dot on a surface near the orifice, the gas flow must be terminated at a precise time. Accordingly, an accurate control mechanism is required to regulate precisely the amount of deposition fluid drawn through the orifice. Conventional spray painting systems have lacked such accurate control capability.